Biological Treatment Practice Questions for Washington Level II

1. Question 1

   Organic load rises, airflow stays steady, and basin DO falls. What relationship best explains this?

   1. The higher load increased biological oxygen use
   2. The higher load reduced every organism's oxygen need
   3. The unchanged airflow guaranteed unchanged DO
   4. The lower DO proves the probe is faulty
   Show the answer

   Answer: A. The higher load increased biological oxygen use

   More biodegradable material can increase microorganism activity and oxygen demand when air supply does not change.

2. Question 2

   Effluent ammonia rises while aeration-basin DO remains normal, and basin pH and alkalinity are trending downward. What should the operator review first?

   1. Aeration rate, diffuser pattern, and blower output.
   2. pH, alkalinity supply, and nitrification loading trend.
   3. RAS flow, clarifier blanket, and return concentration.
   4. WAS flow, solids inventory, and wasting schedule.
   Show the answer

   Answer: B. pH, alkalinity supply, and nitrification loading trend.

   Nitrification consumes alkalinity and is inhibited as pH falls, even when oxygen remains adequate.

3. Question 3

   A verified portable meter shows changing dissolved oxygen at the same location where the online display remains fixed. A simulator applied at the transmitter input causes the displayed value to change normally. Which condition is most likely?

   1. The aeration demand is varying faster than the controller setpoint.
   2. The portable meter is responding to a different sampling depth.
   3. The display has lost communication with the control system.
   4. The online probe is fouled, damaged, or not responding to the process.
   Show the answer

   Answer: D. The online probe is fouled, damaged, or not responding to the process.

   A responsive transmitter/display path and a verified colocated meter isolate the problem to the online sensing element.

4. Question 4

   Which microscopic observation is most consistent with a stable activated-sludge process treating its normal load?

   1. Mostly amoebae with very little organized floc.
   2. Abundant stalked ciliates attached to developed floc.
   3. Numerous flagellates dispersed outside weak floc.
   4. Dominant free-swimming bacteria with no visible floc.
   Show the answer

   Answer: B. Abundant stalked ciliates attached to developed floc.

   A developed floc structure with stalked ciliates is commonly associated with a relatively stable, well-established activated-sludge population.

5. Question 5

   When nitrification becomes more complete under otherwise stable conditions, which effluent trend is generally expected?

   1. Ammonia rises while nitrate falls.
   2. Ammonia rises while nitrate rises.
   3. Ammonia falls while nitrate falls.
   4. Ammonia falls while nitrate rises.
   Show the answer

   Answer: D. Ammonia falls while nitrate rises.

   Nitrification oxidizes ammonia to nitrite and then nitrate, so more complete nitrification generally lowers ammonia and raises nitrate.

Operator Master has 11 Level II biological treatment questions, free, with an explanation after every answer.

• Plant Operations35 questions
• Math and Calculations21 questions
• Pumps and Hydraulics18 questions
• Laboratory9 questions
• Disinfection7 questions
• Solids Handling7 questions
• Secondary Clarification5 questions
• Primary Treatment3 questions
• Grit Removal2 questions